1. Field of the invention
This invention relates to an oil pressure supply valve, and more specially to an oil pressure supply valve for a traction control system, the structure of which is simple and small in size.
2. Description of the Prior Art
In a traction control system, in order to prevent the driving wheels from slipping when excessive driving force is transferred to them or when the car initially accelerates on a slippery road, slip signals of the driving wheels are transferred from a speed sensor installed on the driving wheels to a controller. After the controller receives the slip signals, it provides adequate braking force to the driving wheels by increasing or decreasing the driving force or reducing the engine power without depressing the brake, so that slipping of the driving wheels is prevented.
In a conventional traction control system, as shown in FIG. 1, an oil pressure supply valve 90 is provided. When a traction control system operates, because a TC (Traction Control) valve 100 is closed, the brake oil discharged from a master cylinder 20 is not supplied directly to a pump 40. Instead, the oil flows to the pump 40 via the oil pressure supply valve 90 and is supplied to a wheel cylinder 60, so that an adequate driving force is applied. But when a brake 10 is depressed, the oil pressure is not supplied to the pump 40 because the oil pressure supply valve 90 is closed, but flows to the wheel cylinder 60 via a check valve 30, so that the excessive oil pressure caused by depressing the break 10 is prevented from being transferred to the pump 40. The elements that are indicated by the numerals 50 and 70 are check valves, and 80 is a low pressure tank.
FIG. 4 shows the structure of a conventional oil pressure supply valve for a traction control system.
In a conventional oil pressure supply valve, a master cylinder connection passage 202 and a pump inlet connection passage 203 are formed perpendicular to each other in a body 201, and passages 204,205 and 206 connect the two connection passages 202 and 203. At the lower portion of the body 201 is provided a plunger 215 supported by a spring 216, and at the top of and integrally formed with the plunger 215 is a push rod 214, which passes through the passage 205 and extends to the passage 204. A ball valve 213 provided inside the passage 204 contacts or separates from a valve seat 211 formed at the end of the passage 204 because the movement of the push rod 214 and the ball valve 213 up and down together is governed by the spring 216 and the brake oil pressure. Accordingly, the valve is opened or closed.
In such an oil pressure supply valve, when the traction control system operates, because the resilient force of the spring 216 supporting the plunger 215 is larger than the pressure of the brake oil flowing to the body 201 via the master cylinder connection passage 202, the push rod 214 of the plunger 215 is protruded inside the passage 204. This causes the ball valve 213 to separate from the valve seat 211, which reroutes the brake oil discharged from the master cylinder connection passage 202 to the pump inlet connection passage 203 via the passages 204,205 and 206. From the pump inlet connection passage 203 the brake oil is then supplied to the wheel cylinder via the pump, thereby providing adequate driving force for preventing the driving wheels from slipping when the car is started or accelerated on a slippery road, and for controlling the cornering skid when the car drives around a corner.
However, when a driver depresses the brake because of the driving instability caused by the slipping of the driving wheels, the brake oil pressure discharged from the master cylinder passage 202 becomes larger than the resilient force of the spring 216 and presses the plunger 215 down. Therefore, the ball valve 213 contacts the valve seat 211 to block the passages 204 and 205, thereby preventing excessive oil pressure from being transferred to the pump.
When the brake pedal is then released, as the oil pressure discharged from the master cylinder connection passage 202 is reduced, the spring 216 moves the push rod 214 of the plunger 215 up. Since, the ball valve 213 separates from the valve seat 211, the brake oil discharged from the master cylinder connection passage 202 flows to the pump inlet connection passage 203 via the passages 204,205 and 206 and is supplied to the wheel cylinder.
In a conventional oil pressure supply valve, because the push rod 214 supporting the ball valve 213 is located inside the passage 205, the flowing volume of the brake oil to the pump is relatively small. To solve this problem, the diameter of the passage 205 can be made larger, but as the passage 205 gets larger, the ball valve 213 and the valve seat 211 must also increase in size. Therefore, a conventional oil pressure supply valve has a disadvantage in that the external shape of the valve becomes large and the structure complicated, when it is made large enough to properly accommodate the brake oil flow necessary for braking.